This application relates to the art of conduit joints and, more particularly, to conduit joints that include a locking strap for preventing separation of the joint. The invention is particularly applicable to bell and spigot joints between end portions of cylindrical pipe and will be described with specific reference thereto. However, it will be appreciated that certain features of the invention have broader aspects and can be used in other types of joints.
A common locking strap joint between a bell and spigot includes axially aligned circumferential grooves that form a circumferential locking strap passage between the inwardly facing cylindrical surface of the bell groove and the outwardly facing cylindrical surface of the spigot groove for receiving a locking strap which is inserted into the passage through an entrance opening in the wall of the bell. During handling and installation of the pipe, the locking strap may become dislodged from its position within the aligned grooves between the bell and spigot by withdrawal thereof through the entrance opening in the wall of the bell. This may result in separation of the joint if the locking strap is completely displaced or may significantly weaken the strength of the joint if the locking strap is partially displaced.
It would be desirable to have an efficient arrangement for minimizing the possibility of unintentional locking strap withdrawal once it has been fully inserted into the passage formed by the aligned circumferential grooves between the bell and spigot.
A joint of the type described includes a locking strap having at least one projection that frictionally engages a surface of the locking strap passage for resisting withdrawal of the locking strap from the passage.
In accordance with another aspect of the application, an entrance opening in the wall of the bell to the locking strap passage includes an abutment that is engageable by a locking strap shoulder when the locking strap is fully inserted into the locking strap passage. Engagement between the abutment and shoulder prevents unintentional withdrawal of the locking strap from the locking strap passage through the entrance opening.
In accordance with the present application, a bell and spigot joint includes an outer circumferential spigot groove axially aligned with an inner circumferential bell groove. The aligned grooves provide a locking strap passage for receiving a circumferentially-split generally circular locking strap that is insertable into the passage through a passage entrance opening in the wall of the bell.
In a preferred arrangement, the projection on the locking strap is a crushable rib that provides high frictional interference between the locking strap and a surface of the passage in which it is received.
In one arrangement, the crushable rib extends longitudinally of the locking strap adjacent the tail end thereof and is centered between the locking strap sides. In another arrangement, there are two spaced-apart transverse projection ribs on the outer locking strap surface and a single projection rib on the inner locking strap surface at a location intermediate the two ribs. With this arrangement, the locking strap itself is deformed on the opposite side thereof from the ribs into firm engagement with the inner and outer surfaces of the locking strap passage.
In accordance with another aspect of the application, the entrance opening to the locking strap passage in the wall of the bell includes an abutment engageable by a shoulder on the tail end portion of the locking strap once the locking strap is fully inserted into the locking strap passage. Engagement between the abutment and the shoulder prevents unintentional separation of the locking strap from the locking strap passage. The tail end portion of the locking strap may be outwardly displaced to separate the shoulder from the abutment for allowing withdrawal of the locking strap from the locking strap passage.
The shoulder may be on a trailing surface of a barb that projects from the underside of the locking strap. A cam surface on the opposite side of the locking strap from the barb cooperates with an upper edge of the entrance opening in the wall of the bell to hold the barb shoulder in engagement with the abutment.
It is a principal object of the present invention to provide an improved bell and spigot locking strap joint.
It is another object of the invention to provide an improved locking strap for use with bell and spigot locking strap joints.
It is a further object of the invention to provide improved arrangements for inhibiting withdrawal of a locking strap from a locking strap passage in a bell and spigot locking strap joint.